The present invention relates generally to wind turbines, and more particular to low resistance, vertical axis wind turbines that utilize a unique airfoil design to enhance rotation in winds from a single direction, multiple directions including winds blowing from directly above, and cyclonic winds.
In recent years there has been a dramatic increase in the demand for energy in all forms including fuels and electricity for heating, lighting, transportation and manufacturing processes due to the world's population rapidly increasing, the supply and price-volatility problems of using petroleum and other “fossil” fuels for energy, and the accelerated technological development of large sectors of the world. Despite the construction of hydroelectric facilities and the development of fossil fuel resources at a rapid rate, it has become increasingly evident these efforts are inadequate to keep pace with the growing population's demand. First, fossil fuels such as oil and natural gas are increasingly becoming higher in cost and their availability is limited. Second, the hope that nuclear power would soon lead to a rapid solution of the energy dilemma has been tempered by environmental and safety concerns.
In the face of these growing demands and the resulting research in many fields of energy, wind energy has once again become the focus of such research, in part because the source of such energy, namely wind, is readily available to every country in the world in virtually unlimited quantities, subject only to use of wind turbines or other devices capable of converting the motive force of the wind into energy in a form usable by modern technologies. The interest in the development and harnessing of wind energy for use in homes and factories in the form of electricity is rising as with the rising costs and prices of traditional fossil fuel energy. Wind energy is also desirable because it can be converted to practical use without environmental contamination or chemical air pollution concerns.
One method of converting wind energy to practical use is through the use of a wind turbine. Traditional wind turbines, including what is historically known as a windmill, are horizontal axis wind turbines (HAWTs), wherein blades or vanes are secured to a horizontally supported shaft. As wind impinges on the blades, the horizontal shaft rotates, which rotation can then be translated into electric energy. Typically, the horizontal shaft itself pivots about a horizontal axis (hence the “horizontal axis wind turbine” name) so that the shaft and blades can pivot with the prevailing wind direction so that the shaft and blades can change their orientation as the winds change direction. One drawback to HAWTs is the inefficiencies caused by friction arising from the supported shaft. HAWT turbines utilize bearings for turning, and such bearings can wear out and need replacement. An additional drawback to HAWT turbines is that only the prevailing wind from a single direction can be “harnessed” at any one time to generate energy, so that the HAWT design can be inefficient or the blades and associated gearing can be damaged in changeable or turbulent winds, due to torque. Another drawback is that HAWT wind turbines may not turn or may need mechanical assistance to begin turning, if the wind speed is too low to counter the inertia of the HAWT rotator and bearings.
More recent developments in wind turbine technology have focused on vertical axis wind turbines (VAWTs), wherein a foil or vane is mounted on a vertically supported axis. Because of their vertical axes of rotation, VAWTs do not require alignment with the direction from which the wind is blowing. Prior art VAWTs include drag-based designs that move by being pushed by the wind, and lift-based designs which move from lift that is developed by the vanes. These prior art designs suffer inefficiencies due to drag during part of the rotation, which is a consequence of the vane shapes and gearing.
Various attempts have been made in the prior art to develop a method for utilizing wind energy by use of a vertical axis type windmill/wind-turbine. For example, U.S. Pat. No. 226,357 issued Apr. 6, 1880, describes a drag-based vertical axis windmill design. This patent teaches a windmill design that utilizes flat “fans” mounted pivotally on a support structure to catch wind and cause the support structure to rotate. As the fans orbit the vertical axis, they pivot between a downwind orientation, presenting a broad area that catches the wind, and an upwind orientation in which a narrower profile passes before the wind in order to create less drag. One drawback to this design is that the flat fans are not very aerodynamic in design and thus operation is rough and slow, with the fans being pulled out of position by centrifugal force. The fans provide drive only intermittently during a somewhat small portion of each rotation. Further, upright structural bars at the outermost ends of the fans obstruct airflow and prevent the system from achieving rotor speeds faster than wind speed.
Another illustration of the development of VAWT's is found in U.S. Pat. No. 2,038,467 issued on Apr. 21, 1936, wherein there is described a vertical axis drag-based windmill design that employs flat “vanes” on a rotating frame. The two-phase vanes are balanced on the vertical axis so that they pivot about 170 degrees between a high-drag position downwind and a low-drag position upwind. The windmill exhibits drag rotation over 180 degrees of each revolution, but vane interference of the upwind vane over the downwind vane in its wind shadow reduces overall effectiveness. Thus, the effective transference of force occurs over less than 180 degrees.
Other VAWT prior art attempts utilizing a lift-based design. For example, U.S. Pat. No. 4,383,801 issued May 17, 1983, discloses a lift-based VAWT that includes vertically arranged vanes mounted pivotally on a rotating base. As the vanes catch the wind and move the support, they orbit the vertical axis. A wind-vane-controlled pitch adjustment continually orients the airfoils relative to the wind direction. The device detects wind direction by means of a vane and positions the controlling pitch flange accordingly. One drawback to this patent is that the positioning of the airfoils is truly effective only in the directly windward and directly leeward positions, using crosswind lift force in both cases.
Another example of a lift-based VAWT is U.S. Pat. No. 6,688,842 issued Feb. 10, 2004. In this patent, a VAWT with “free flying” airfoils is taught, wherein the airfoils are self-positioning according to the local dynamic conditions to which they are subjected, thereby creating a condition of equilibrium in order to make the “engine” more efficient. More specifically, the patent teaches a vertical axis wind engine with a rotor mounted on a base for rotation about a vertical axis. One or more airfoil(s) is mounted on the rotor so that it is free to pivot between preset first and second limits of pivotal movement (e.g., set by stop mechanisms). That arrangement enables the airfoil to align according to the wind as it orbits the vertical axis, thereby achieving better conversion of wind energy to useable rotational energy by combining lift and drag characteristics at low speeds and shifting to lift-only characteristics at rotor speeds approaching or exceeding local wind speed. Wind forces and armature-constraining action establish airfoil positions. The airfoils rotate freely through an arc of approximately 90 degrees, bounded by stop mechanisms. The span of travel is from a radial line along the mounting arm (radially aligned relative to the vertical axis) to a perpendicular position (tangentially aligned relative to the vertical axis). This prior art design allows for each airfoil to set its own instantaneous angle and to adjust to conditions of relative wind, wind shift, and so forth occurring outside and within the wind engine, “without external adjustments or mechanisms, wind vanes, centrifugal governors, or other controlling devices.” Individual airfoils adjust to local conditions based on changes of rotor speed, turbulence, true relative wind, and other factors affecting each of them independently. A drawback to this design, however, is that the efficiency is limited because the airfoils rotate through only about a 90 degree arc (out of a possible 360 degrees) and are constrained by stops.
A further drawback to the various VAWTs of the prior art is similar to those inefficiencies found in the HAWTs, namely that there is a relatively large amount of weight carried by the bearings that support vertically rotating component of the VAWTs. In addition to the loss of energy resulting from the friction between the relative components, this leads to the need to replace bearings on a regular basis.
Notwithstanding the foregoing, in recent years various electricity generating utilities have conceived of the need to promote “distributed generation” of electricity as a means of decentralizing the commercial electricity grid, which suffers from centralized generation plants and switching and transmission lines that are sometimes old and in poor repair, such that a grid may become unstable and prone to outages of electrical power. In response and as a means of diminishing the risk of rising energy costs to the consumer, it has become more prevalent to generate electricity from renewable sources of energy using decentralized devices located on buildings or on land or in yards belonging to small commercial companies or even individuals. While it is most common in remote locations that this renewable-sourced electricity is generated solely for local consumption, in other locations where a grid connection is available, electrical utilities are offering “net metering”. Net metering equipment allows “co-generation” of electrical power, such that both the utility and the end user can generate electricity. Since the bi-directional electric meter accurately registers the flow of electricity in both directions, net metering not only helps to maximize the value of distributed generation, but does so with little cost to the consumer. In other words, the meter spins forward when the customer uses more electricity than is being produced, and spins backward when the customer is producing more electricity than is needed.
Therefore, as interest in co-generation grows, there is a need for better, more efficient renewable-energy electricity generating devices. An improved VAWT capable of harnessing wind from a full 360 degrees of rotation about the vertical axis would be one such device. Desirably, the VAWT should also harness vertically impinging wind and cyclonic wind. The VAWT also should minimize inefficiencies arising from frictional losses. Preferably, the VAWT materials should maximize strength and durability but have a low cost of manufacture so as to be economically available to consumers for use in individual households.